I think Hinata and Rias could be paired up in some way. Hinata's gentle nature and her strong loyalty could complement Rias' leadership and determination. They might form an unexpected friendship or even a strategic alliance within the fanfiction's plot.
Another possible pairing could be Sasuke and Vali. They are both powerful and somewhat anti - hero - like characters. Their rivalry or partnership could be a central part of the story. They might start off as enemies but then find common ground as they face greater threats in the combined Naruto and DxD universe.
Sasuke and Tex might be likely to be paired up. Both are strong and somewhat brooding characters. Sasuke's quest for power could be paralleled with Tex's own abilities and her role in the Red vs Blue universe. They might engage in some intense battles or even end up having to work together against a common enemy, leading to some interesting character development for both of them.
Another possible pairing could be Sasuke and Elsa. Sasuke has his own dark past and a brooding personality. Elsa also has her own internal struggles with her powers. They could bond over their shared experiences of having to control something within themselves that others might fear. And their cool and somewhat aloof demeanors could make for an interesting dynamic.
Naruto and Bella could be an interesting pair. Naruto's energetic and positive nature could contrast with Bella's more introverted and moody self. It could create a unique dynamic where Naruto tries to cheer up Bella and she, in turn, shows him the more complex emotional side of the Twilight world.
Well, I think Green Lantern and Rock Lee would be an interesting pair. Green Lantern's power of creating constructs with his ring could be used in creative ways along with Rock Lee's taijutsu. Also, Wonder Woman and Hinata could be paired. Wonder Woman's combat skills and Hinata's Byakugan - enhanced fighting style would make for a great combination. And Flash and Kiba with his dog Akamaru could be a fun pair, with Flash's speed and Kiba's speed - based ninja techniques.
Well, Clarisse might be paired with a more aggressive Doom character. She's a fierce warrior in the Percy Jackson series. They could form a powerful duo, fighting side by side against the common enemies. Also, Tyson could be paired with a strong, hulking character from Doom. Tyson is a Cyclops with great strength, and finding a counterpart in Doom that shares that physical power would create an interesting dynamic in the fanfiction.
Naruto and Bart could be a likely pair. Both are mischievous in their own ways. Naruto is always getting into trouble with his pranks in the ninja academy, and Bart is constantly causing chaos in Springfield. They could get up to all sorts of antics together, like pulling pranks on the other characters in both universes.
Sasuke and Sein could be an unexpected but fascinating pair. Sasuke's brooding and powerful presence might contrast with Sein's pure and guiding spirit. Their interactions could lead to some great character development for both of them.
Sasuke could also be a character who is frequently betrayed in these fanfictions. Given his complex personality and his history of being both a loner and a seeker of power, he might be lured into dangerous alliances in the DxD world. And his partners in the DxD world could betray him when they realize they can't control him or when his power becomes a threat to them.
Naruto and Issei are very likely crossover characters. Naruto, with his strong will and powerful ninja skills, would be an interesting contrast to Issei, the perverted but also determined protagonist of Highschool DxD. Another likely pair could be Sasuke and Vali. Both are brooding, powerful characters with their own agendas. Sasuke's Sharingan abilities could have some really cool interactions with Vali's powers in the context of this fanfiction. And of course, Kakashi could be a great crossover with some of the more strategic characters in Highschool DxD, like Sona, as he is known for his intelligence and combat skills.
Naruto is definitely a main character. His presence and his god - like abilities are what make this fanfiction unique. Then, there could be characters like Rias Gremory. She's an important figure in the DxD world, and her relationship with Naruto could range from being an ally to a potential love interest. Also, characters like Akeno Himejima could be involved. She might be curious about Naruto's powers and his different way of doing things compared to the DxD characters.